The present technique relates to a memory device for storing data and reading data from itself.
The error correcting code (ECC) technique and cyclic redundancy check (CRC) technique have been used on a hard disk drive (HDD) to guarantee data during reading. The ECC technique is used to correct data. The CRC technique is used to verify authenticity of data. The CRC technique detects the reading of data on a sector different from the one predicted, based on data unique to sector such as a logical block address (LBA).
For example, Japanese Laid-open Patent Publication No. 2004-192676 discloses a magnetic disk device that guarantees a magnetic recording function by detecting a magnitude of crosstalk between tracks, and performing a status determination as to whether a magnetic recording function is normal or not. For another example, Japanese Laid-open Patent Publication No. 5-224833 discloses a data guarantee method for guaranteeeing data by verifying in a reading operation or a writing operation that an external memory device that reads or writes data on a magnetic disk device or the like has read correctly data at a target address.
Track spacing gets narrow as a storage capacity and a recording density of HDD increase. An unpredictable track can be present between tracks because of a difference between core widths of a write head and a read head, the effect of a single platter servo track writing (STW), and other factors. Data may be written on the unpredictable track. Even if such a track is detected and the data is then written back into an originally intended track, duplicate tracks having the same sector information are present. If data is read out from the unpredictable track because of residual vibration or the like, no sector fault can be detected and garbled data may occur.
The malfunction is described below with reference to FIG. 7, wherein D1 through D3 are predictable tracks while D1′ through D3′ are unpredictable tracks. If data is written into sectors on tracks D1′ through D3′, the data is then detected and written into the correct tracks (D1 through D3). When the HDD is used later on, new data may be written on the tracks D1 through D3. The new data on tracks D1 through D3 are now different from the data on tracks D1′ through D3′ (see an upper portion of FIG. 7).
In this state, data on tracks D1 through D3 should be read during a reading operation. But if data is read out from the tracks D1, D2 and D3′ because of residual vibration as represented by an arrow in a lower portion of FIG. 7, data garbling thus takes place with any sector error going unnoticed.